HYDRAULIC APPARATUS FOR CONSTRUCTION MACHINES

A hydraulic apparatus for a construction machine, which is adapted to prevent the number of revolutions of an engine from increasing when the flow of the fluid discharged by a variable displacement hydraulic pump driven by the engine is cut off. The hydraulic apparatus comprises a proportional solenoid (11) connected to a fuel supply control lever (13) so as to vary the horsepower characteristics of the engine, which are set by the action of a governor (12) based on manipulated variable of the fuel supply control lever (13) when the flow of the fluid discharged by said pump is cut off, and a controller (10) for controlling the proportional solenoid (11). In this apparatus, a decrement (.DELTA.Nr) in a target number of revolutions per minute (Nr) of the engine, which can be obtained by subtracting a target number of revolutions per minute (Nrb) of the engine at the desired engine horsepower characteristics (l.sub.2) from a target number of revolutions per minute (Nra) at the initial engine horsepower characteristics (l.sub.1) is computed, and said proportional solenoid (11) is operated in accordance with this decrement.